src/code/early-raw-slots.lisp

   1 ;;;; This software is part of the SBCL system. See the README file for
   2 ;;;; more information.
   3 ;;;;
   4 ;;;; This software is derived from the CMU CL system, which was
   5 ;;;; written at Carnegie Mellon University and released into the
   6 ;;;; public domain. The software is in the public domain and is
   7 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
   8 ;;;; files for more information.
   9
  10 (in-package "SB!KERNEL")
  11
  12 ;;; STRUCTURE-OBJECT supports placement of raw bits within the object
  13 ;;; to allow representation of native word and float-point types directly.
  14
  15 ;;; Historically the implementation was optimized for GC by placing all
  16 ;;; such slots at the end of the instance, and scavenging only up to last
  17 ;;; non-raw slot. This imposed significant overhead for access from Lisp,
  18 ;;; because "is-a" inheritance was obliged to rearrange raw slots
  19 ;;; to comply with the GC requirement, thus forcing ancestor structure
  20 ;;; accessors to compensate for physical structure length in all cases.
  21 ;;; Assuming that it is more important to simplify Lisp access than
  22 ;;; to simplify GC, we use a more flexible strategy that permits
  23 ;;; descendant structures to place new slots anywhere without changing
  24 ;;; slot placement established in ancestor structures.
  25 ;;; The trade-off is that GC (and a few other things - structure dumping,
  26 ;;; EQUALP checking, to name a few) have to be able to determine for each
  27 ;;; slot whether it is a Lisp descriptor or just bits. This is done
  28 ;;; with the LAYOUT-BITMAP of an object's layout.
  29 ;;; The bitmap stores a '1' for each bit representing a raw word,
  30 ;;; and could be a BIGNUM given a spectacularly huge structure.
  31
  32 ;;; Also note that there are possibly some alignment concerns which must
  33 ;;; be accounted for when DEFSTRUCT lays out slots,
  34 ;;; by injecting padding words appropriately.
  35 ;;; For example COMPLEX-DOUBLE-FLOAT *should* be aligned to twice the
  36 ;;; alignment of a DOUBLE-FLOAT. It is not, as things stand,
  37 ;;; but this is considered a minor bug.
  38
  39 ;; To utilize a word-sized slot in a defstruct without having to resort to
  40 ;; writing (myslot :type (unsigned-byte #.sb!vm:n-word-bits)), or even
  41 ;; worse (:type #+sb-xc-host <sometype> #-sb-xc-host <othertype>),
  42 ;; these abstractions are provided as soon as the raw slots defs are.
  43 ;; 'signed-word' is here for companionship - slots of that type are not raw.
  44 (def!type sb!vm:word () `(unsigned-byte ,sb!vm:n-word-bits))
  45 (def!type sb!vm:signed-word () `(signed-byte ,sb!vm:n-word-bits))
  46
  47 ;; information about how a slot of a given DSD-RAW-TYPE is to be accessed
  48 (defstruct (raw-slot-data
  49             (:copier nil)
  50             (:predicate nil))
  51   ;; the type specifier, which must specify a numeric type.
  52   (raw-type (missing-arg) :type symbol :read-only t)
  53   ;; What operator is used to access a slot of this type?
  54   (accessor-name (missing-arg) :type symbol :read-only t)
  55   (init-vop (missing-arg) :type symbol :read-only t)
  56   ;; How many words are each value of this type?
  57   (n-words (missing-arg) :type (and index (integer 1)) :read-only t)
  58   ;; Necessary alignment in units of words.  Note that instances
  59   ;; themselves are aligned by exactly two words, so specifying more
  60   ;; than two words here would not work.
  61   (alignment 1 :type (integer 1 2) :read-only t)
  62   (comparer (missing-arg) :type function :read-only t))
  63
  64 #!-sb-fluid (declaim (freeze-type raw-slot-data))
  65
  66 ;; Simulate DEFINE-LOAD-TIME-GLOBAL - always bound in the image
  67 ;; but not eval'd in the compiler.
  68 (defglobal *raw-slot-data* nil)
  69 ;; By making this a cold-init function, it is possible to use raw slots
  70 ;; in cold toplevel forms.
  71 (defun !raw-slot-data-init ()
  72   (macrolet ((make-comparer (accessor-name)
  73                #+sb-xc-host
  74                `(lambda (x y)
  75                   (declare (ignore x y))
  76                   (error "~S comparator called" ',accessor-name))
  77                #-sb-xc-host
  78                ;; Not a symbol, because there aren't any so-named functions.
  79                `(named-lambda ,(string (symbolicate accessor-name "="))
  80                     (index x y)
  81                   (declare (optimize speed (safety 0)))
  82                   (= (,accessor-name x index)
  83                      (,accessor-name y index)))))
  84     (let ((double-float-alignment
  85             ;; white list of architectures that can load unaligned doubles:
  86             #!+(or x86 x86-64 ppc arm64) 1
  87             ;; at least sparc, mips and alpha can't:
  88             #!-(or x86 x86-64 ppc arm64) 2))
  89      (setq *raw-slot-data*
  90       (vector
  91        (make-raw-slot-data :raw-type 'sb!vm:word
  92                            :accessor-name '%raw-instance-ref/word
  93                            :init-vop 'sb!vm::raw-instance-init/word
  94                            :n-words 1
  95                            :comparer (make-comparer %raw-instance-ref/word))
  96        (make-raw-slot-data :raw-type 'single-float
  97                            :accessor-name '%raw-instance-ref/single
  98                            :init-vop 'sb!vm::raw-instance-init/single
  99                            ;; KLUDGE: On 64 bit architectures, we
 100                            ;; could pack two SINGLE-FLOATs into the
 101                            ;; same word if raw slots were indexed
 102                            ;; using bytes instead of words.  However,
 103                            ;; I don't personally find optimizing
 104                            ;; SINGLE-FLOAT memory usage worthwile
 105                            ;; enough.  And the other datatype that
 106                            ;; would really benefit is (UNSIGNED-BYTE
 107                            ;; 32), but that is a subtype of FIXNUM, so
 108                            ;; we store it unraw anyway.  :-( -- DFL
 109                            :n-words 1
 110                            :comparer (make-comparer %raw-instance-ref/single))
 111        (make-raw-slot-data :raw-type 'double-float
 112                            :accessor-name '%raw-instance-ref/double
 113                            :init-vop 'sb!vm::raw-instance-init/double
 114                            :alignment double-float-alignment
 115                            :n-words (/ 8 sb!vm:n-word-bytes)
 116                            :comparer (make-comparer %raw-instance-ref/double))
 117        (make-raw-slot-data :raw-type 'complex-single-float
 118                            :accessor-name '%raw-instance-ref/complex-single
 119                            :init-vop 'sb!vm::raw-instance-init/complex-single
 120                            :n-words (/ 8 sb!vm:n-word-bytes)
 121                            :comparer (make-comparer %raw-instance-ref/complex-single))
 122        (make-raw-slot-data :raw-type 'complex-double-float
 123                            :accessor-name '%raw-instance-ref/complex-double
 124                            :init-vop 'sb!vm::raw-instance-init/complex-double
 125                            :alignment double-float-alignment
 126                            :n-words (/ 16 sb!vm:n-word-bytes)
 127                            :comparer (make-comparer %raw-instance-ref/complex-double))
 128        #!+long-float
 129        (make-raw-slot-data :raw-type long-float
 130                            :accessor-name '%raw-instance-ref/long
 131                            :init-vop 'sb!vm::raw-instance-init/long
 132                            :n-words #!+x86 3 #!+sparc 4
 133                            :comparer (make-comparer %raw-instance-ref/long))
 134        #!+long-float
 135        (make-raw-slot-data :raw-type complex-long-float
 136                            :accessor-name '%raw-instance-ref/complex-long
 137                            :init-vop 'sb!vm::raw-instance-init/complex-long
 138                            :n-words #!+x86 6 #!+sparc 8
 139                            :comparer (make-comparer %raw-instance-ref/complex-long)))))))
 140
 141 #+sb-xc-host (!raw-slot-data-init)
 142 #+sb-xc
 143 (declaim (type (simple-vector #.(length *raw-slot-data*)) *raw-slot-data*))
 144
 145 ;; DO-INSTANCE-TAGGED-SLOT iterates over the manifest slots of THING
 146 ;; that contain tagged objects. (The LAYOUT does not count as a manifest slot).
 147 ;; INDEX-VAR is bound to successive slot-indices,
 148 ;; and is usually used as the second argument to %INSTANCE-REF.
 149 ;; :PAD, if T, includes a final word that may be present at the end of the
 150 ;; structure due to alignment requirements.
 151 ;; LAYOUT is optional and somewhat unnecessary, but since some uses of
 152 ;; this macro already have a layout in hand, it can be supplied.
 153 ;; [If the compiler were smarter about doing fewer memory accesses,
 154 ;; there would be no need at all for the LAYOUT - if it had already been
 155 ;; accessed, it shouldn't be another memory read]
 156 ;;
 157 (defmacro do-instance-tagged-slot ((index-var thing &key layout (pad t)) &body body)
 158   (with-unique-names (instance bitmap limit)
 159     `(let* ((,instance ,thing)
 160             (,bitmap (layout-bitmap ,(or layout `(%instance-layout ,instance))))
 161             (,limit ,(if pad
 162                          ;; target instances have an odd number of payload words.
 163                          `(logior (%instance-length ,instance) #-sb-xc-host 1)
 164                          `(%instance-length ,instance))))
 165        (do ((,index-var sb!vm:instance-data-start (1+ ,index-var)))
 166            ((>= ,index-var ,limit))
 167          (declare (type index ,index-var))
 168          (unless (logbitp ,index-var ,bitmap)
 169            ,@body)))))